1. Field of the Invention
This invention relates to a noncontact type tonometer for measuring eye pressure by projecting fluid towards a cornea.
2. Prior Art of the Invention
As a tonometer of this type, an air puff type tonometer is known, for example. In this conventional tonometer, various alignment works must be performed before measurement, such as, for example, alignment of a working position of a main instrument and a vertical or horizontal position thereof with respect to an eye to be tested.
Subsequently, an air pulse is projected towards the cornea of the eye to be tested through an air pulse projecting nozzle, and light is projected towards the cornea by a light projector.
Then, the projected light is reflected off the cornea, and, when the light quantity entering into a light receiving device becomes maximum, the fact that the cornea has been made applanated by the air pulse is confirmed and the measurement is finished.
However, in a conventional tonometer of this type, the examiner is busy in observing an optically enlarged corneal portion during alignment verification and measurement and, therefore, is unable to observe the entire eye to be tested. Therefore, the examiner does not know the state of the eye under which the measurement is being carried out.
Therefore, even if the light projected by the light projector is reflected by an anterior portion of the eye and enters into the light receiving device, when, for example, an eyelash or an eyelid (anterior portion) hangs over the eye to be tested and by this reason, the light quantity received by the light receiving device becomes maximum, there is a risk that examiner may overlook it. Thus, the conventional tonometer is problematical in reliability and accuracy of measurement.